Control mechanism and apparatus for an ice eliminating system having inflatable members and heater elements



Feb. 23, 1954 C. H. M INTYRE CONTROL MECHANISM AND APPARA SYSTEM HAV 2,670,161 N INFLATABL M TUS FOR AN ICE ELIMINATING E EMBERS AND HEATER ELEME Filed Aug. 10, 1951 NTS 2 Sheets-Sheet l ENGINE a SUCTI N LINE sucnou 7 RIVEN on SEPA ifn fuz AND Al 3' 6 FILTER Q 0 37 I N u ENGINE on VEN 51%: 82315", I ALTERNATOR- BANK z 9 522 INFLATABLE BOOTS 4 REVEEREIPJG 4| -42 R A 1 TO RESISTOR TO R5 5 R HEATER umrs l 8 3?]??? "ma UNITS lsrmauruc Ji l I II MR PRESSURE I 1 I! lijfifi? ELECTRIC CONTROL LINE A Q v 7 INVENT0R. CHARLES H. MAC/NTVRE 2,670,161 TING 2 Sheets-Sheet 2 N ICE ELIMINA HEATER ELEMENTS INVENTOR AQ L ES H. MAC/NTVPE D APPARATUS FOR A H. M INTYRE FLATABLE MEMBERS AND YSTEM HAVING IN CONTROL MECHANISM 15km: mew-mum S Filed Aug. 10, 1951 Feb. 23, 1954 Patented Feb. 23, 1954 CONTROL. MECHANISM AN D- APPARATUS- FOR AN ICE, ELIMINATING SYSTEM HAV- INGr INFLATABLE MEMBERS AND HEATER ELEMENTS.

Charles H; MacIntyre, Hasbrouck Heights, N'. J., assignor:toBendixAviation Corporation, Testers-- a corporation ofl'llelaware Application August 10, 1951, Serial N 0. 241,356

4 Claims. I The-present invention relates to improvements lathe operatingmechanismfor an ice eliminating systemof the electro-pneumatic type such as disclosed in Taylor U; S; Patent No; 2,418,205-granted April 1, 1947 and assigned-toTheB. F1 Goodrich Company and which includes distortable inflatable members for-removing ice from an airfoil surface of an aircraft in cooperation with electric resistorheater-elements embedded in said mem- The system normally operates with the in flatable member-s continuous cyclic operation through the operation of suitable air distributing valve-mechanism such asdisclosed in' Lawrence etial; U. S-.- Patent No.- 2,515,519grantedJuly 1S, 1950 :and assigned: to" Bendix- Aviation Corporationand which the distributing valve mechanisms are-cyclically operated in accordancewvith a schedule prescribed by the stepper switches of an electronic timersuch as disclosed'in-Lauricella U. S27 Patent No. 2,-444';210=grantedJune-29, 1948 and: assigned to Bendix Aviation Corporation. While the inflatable members normal operation-are in continuous cyclic operation, the heater ments are divided into two banks, each bank consisting of-the ice-eliminatingpanels on one wing oftheaircraft and-half the-empennage, and each bank is normally energized bytheeleetric power suppliedbya-separate-alternator driven by the aircraft-engine.-

An object of the invention is to provide novel means; whereby should either of the aforenoted alternator-s fail; theoutput of the remaining alternator-may be -alternately transferred from one heater bank to the other so as to provide-eilective removal of the ice from the airfoil surfaces.-

Another object of the inventionis-to provide an emergency-controlsystem for the heater elements includinga reversing'switchor transfer relay to alternately switch the remaining alternator from one heater bank to the-other undercontrol ofthe el'eotronictimer for the infiatable ice= eliminating members:

Another object of the invention is to provide an' emergency control systemfor the heater elements effective upon failure of'the power supply for-oneof'the banks of heater elements to causesimultaneous operation of bothheaterelements and inflatable members under-control ofa single timing apparatus so as to prevent the accumulatlon of ice on or the-removal of ice from aerofoil surfaces of an aircraft;

' -'I h'e-"above and-other objects and features of 2; the invention will appear more fullyherematter from a considerationof the following description takenin connection with theaccompanying draw ingswherein one embodimentof the invention is illustrated by way ofexample.

In the drawings:

Figure l is a fragmentary planview: of an: aircraf-tshowing diagrammatically the manner-in which the novel control apparatus is connected into the ice eliminatingsystem:

Figure 2- is a diagrammatic view illustrating an electrical timing circuitembodying: the-invent tion.

Referring to the-drawing'of- Figure 1 there is shown an aircraft. indicated by. the numeral I having an engine 2- and infiatableielements or boots 3 mounted along the leading edge; 015i the plane and of the typeincludingresistor heating elements embedded thereon. The operating mechanism forthe inflatable elements: are: of: a type such as disclosed in the copending application Serial No. 733,960 filed March 11; 1947, by Donald M. Lawrence, U. S. Patent No. 2,. 476,198 granted July 12, 1949 to'Donaldv M:v Lawrence and in'U. S; Patent No. 2,51535-19grantedJi1lY 18, 1950 to Donal'd 'Mf Lawrenceet al.land,a'1l1of which have been assigned to Bendix Aviation Corporation:-

The-engi'ne- 2 is arranged-so as to: drive an aincraft' propeller 5'! An air' pump: Ii is also driven in aconventional manner by; the engine 22 and has provided a suction conduit 1 leadingtothe main suction line 8 through a suitable suction relief valve, as shown;

An air pressure line B lead's from:the pump' Blto the-inl'etofa pressure unloading: valve or device indicated generally by the'numeralf m and which may be of the type disclosed" and claimed: the aforementioned application Serial No. 7331960. The air passes throughthe device in and-into..the outlet conduit 5 2-1 uponzenergization; of; a:. control solenoid provided therein as" explained; in. the applicationcSerial 'No; 7 33;960; During; thefpas. sage of thee-air through. the device i0; .any.- par ticles of oilwhich; may, enter the air from; the pump '6 or other source, is separatedandthelair is filtered of dirt and other extraneousmatter by an oil separator and air. filter provided in the device I 0 asdisclosed and claimed in theILiS. appli cation Serial No. 733,960. The, air flow thus processed, is conducted through the conduit -I2 to the air pressure line IS.

The suction and' air pressure lines -3- and" i5 lead to suitable-air distributor valves l8 having control solenoids I9 shown" diagrammatically in Figure 2 and which are electrically controlled by a timer indicated generally by the numeral 20 so as to operate the inflatable boot elements 3. A plurality of such distributor valves are preferably provided of a type such as disclosed and claimed in the aforenoted U. S. Patent No. 2,515,519. The timer 20 includes as shown in Figure 2 an electronic timer which may be of the type disclosed and claimed in U. S. Patent No. 2,444,210 granted June 29, 1948 to John W. Lauricella and assigned to Bendix Aviation Corporation.

A manually operable switch 25 is arranged to simultaneously close both circuits 25-4! and 29-3Ii to condition the timer 20 for operation, as well as cause the unloading valve of the device 'I to direct air under pressure through line i2 to the pressure line it to condition the same for subsequent operation or" the distributor valves I8. In the system disclosed when switch 25 is opened and operation of the inflatable ice eliminating system terminated the unloading valve of the device it closes the conduit I2 and directs the air flow from the conduit 9 to an overboard dump 3i, as explained in the application Serial No. 733,960.

The unloading valve of the device It has a control solenoid 33, shown schematically in Figure 2, and the device It may be of the type disclosed and claimed in the application Serial No. 733,960 in which the unloading valve is arranged to close the passage I2 and open the discharge passage SI to the passage 9 upon deenergization 0f the solenoid 33, and close the passage 3! to passage t and open the passage I2 to the passage 9 upon energization of the solenoid 33.

In addition to the inflatable elements 3, there are embedded therein suitable electric resistor heater elements 34, shown schematically in Figure 2, and which may be of a type such as disclosed in the Taylor U. S. Patent No. 2,i18,20-5. The energizing power for these electric heating elements is provided by two alternators 35 and 31' driven by the engine 2 and connected through suitable electrical conduits 39 and 6!, respectively, to the heating elements and controlled by switches t3 and 45, as shown in Figure 2. The electric heating elements are divided into two banks, each bank consisting of the heating elements on one wing and half empennage and normally energized by its associated engine driven alternator 35 or 37.

Connected across the lines 39 and M by conductors it and M, respectively, are indicator lights t8 and 59 which may be conveniently mounted in the cabin of the aircraft for ready observation by the pilot of the aircraft to indicate failure of the alternators 35 and 31, respectively.

As shown diagrammatically in Figure 2, the power lines 39 and ill lead to the heater elements 3 1 of the No. l and No. 2 heater banks through a reversing relay i} controlled by a solenoid 52. The solenoid 52 is effective upon energization to actuate relay switch arms 54 so as to transfer the connection of the alternator 35 from the No. 1 bank of resistor heater elements to the N0. 2 bank and to actuate relay switch arms 55 so as to transfer the connection of the alternator 37 from the No. 2 bank to the No. 1 bank or resistor heater elements. When the solenoid 52 is deenergized, the relay switch arms 54 and 5B are spring biased to the position shown so as to connect the alternator 35 to the No. 1 bank and 4 the alternator 31 to the No. 2 bank of resistor heater elements.

The solenoid 52 may be connected by a conductor 6% to a contact 62 controlled by a switch arm 5d manually operable by a suitable-adjustment knob 55 mounted on the panel of the timer 2! The switch arm 64 is in turn connected by a conductor 66 to contacts 68A-F controlled by a rotary switch arm 68 of a stepper relay 69, shown in Figure 2, and the operation of which is hereinafter explained. The contacts tflG-N are also controlled by the rotary switch arm 68 and are open. The rotary switch arm 68 is in turn connected by a conductor in to the conductor 21 leading through the switch 25 to the source of electrical energy 28. The switch arm 66 in addition to controlling contact 62 also cooperates with open contacts ?2 and It.

Thus, upon failure of either alternator 35 or 37, as indicated by its associated indicator light ll or 19 as the case may be, the pilot adjusts the knob 55 to the half on position whereupon switch arm 6d closes contact 82 and the stepper relay switch arm 68 thereupon serves to cycle the reversing switch 50 so as to alternately transfer the output of the remaining alternator first to one bank of heater elements by closing the contacts ttA-F and then to the other bank of heater elements by opening the contacts 68A-F and closing one of the remaining contacts GS-G-N.

Referring now to the drawing of Figure 2, there is shown a system for timing the operation of the stepper relay 59 to normally control the energization of a series of electromagnets [9 which serve to control boot-inflating valves I8 of the ice eliminating system as described and claimed in the aforenoted Lawrence et al. U. S. Patent No. 2,515,519.

The stepper relay 69 may be of a conventional type comprising an electromagnetic winding H2 which controls the movement of an armature I I3 pivotally supported at Ht. A ratchet arm I I5 is pivotally mounted on the armature H3 and is biased into engaging relation with a ratchet wheel Hit by a spring Ill. A second spring H8 biases the armature H3 in a counterclockwise direction into contacting relation with a stop H9. A pawl I20 is biased into engaging relation with the teeth of the ratchet wheel IIB by a spring IZI so as to prevent rotation of the ratchet wheel H8 in a counter-clockwise direction.

It will be readily seen from the foregoing that upon energization of the electromagnet H2 the armature H3 will be pivoted in a clockwise direction in opposition to the force of the spring H8 causing the ratchet arm H5 to engage the next succeeding tooth of the ratchet wheel H6. At the extreme limit of movement of the armature H3 an actuating member I22 carried thereby engages the free end of a leaf spring I23 so as to open the contacts of a switch I24.

The opening of the switch I24 breaks the circuit of the electromagnet I I2, as will be explained; hereinafter, causing de-energization of the electromagnet II'Z, whereupon the spring H8 actuates the armature H3 in a counterclockwise directon causing the pawl H5 to impart an more ment of movement to the ratchet wheel H6 in a clockwise direction.

The ratchet wheel HE is connected through a suitable shaft I25 indicated herein by dotted lines to switch arms 68, I26 and I21. I

The switch arms 68. I26 and I21 are each arof the switch I49 to close contact ranged. to; contact. in: succession; a; series; of: con;- tacts 6ItA'--N-,v I26A1-N. andi min-N. The: switch arms. 68, I26. and I21 move. from. one: contact to the nextsucceeding contactfor each increment of movementzimparted' to the ratchet wheel. M6 by. the stepper relay 69 and upon; one: end. of the switch arm moving out of contactingirelation: with thecontact N, the opposite:end: closes the contact A.

The switch contacts: I25A-N are ,connectedre spectively through suitable electrical conductors to one terminal. of corresponding electromagnets I9. The opposite-terminalof theelectromagnets I9are;-connected.by anelectrical conductor I3I to; the. negative terminal of alsource. of electrical energy 2.8,through a grounded; connectiom The; switch; arm I26 is connecteds by the. con ductor: 21' through the manually operable? control: switch 25v to the positive; terminal of; the source. of electrical energy 28.

The contact I26N is an:open contact so; that upon the switch arm I26, contacting. the same, the; circuit to, all of the electromagnets I9- are open for a purpose which will appear hereinafter;

The switch arm close contacts- I 2 I is arranged to sequentially IZ'IA-N connected to suitableyresistor elements I36. which are in turnconnected at the opposite end to conductor 21 for a purpose which will be explained hereinafter.

The shaft I25 also, drives a cam I28, having portions I29, arrangedto actuate an off normal switch I 31 to an open position upon the switch arms 68, I26 and I2-'I- being positioned so as to close-the respective contacts SBN, I26N and-IZTIN. Upon the switch arms 68, I25 and I2] being adjustedinto contacting'relation with one of the other contacts, the cam I28 permits the switch I31 to close for purposes which will be explained.

A relay winding I38 has one terminal con nected by an electrical conductor I39 through-the normally closed switch I24 and a conductor I40 to the positive terminal of the source of electricalenergy 28 through the control switch 25. The opposite terminal of the winding I38-. is connected. by an electrical'conductor I4I'to-an anode or plate I42 of an electronic valve I43.

The electronic valve I43 has cathodes I44, con-. trol grids I45, shield grids I46, heater or filaments I41 and the plates I42.

The cathodes I44 are connected by a conductor I48,to a manually operable selector switch I49 andthrough a conductor I50to-0necontact I5I of. the off normal switch I3]. The oppositecontact I52 is connected through the, switch arm I3'Iand a grounded conductor I53.to the negative terminal of the source of electrical energy 28.

The switch I49 cooperates with switch contacts I49A-C. A conductor I54 leads from the contact H913 to the conductor I4I so that upon switch arm I49 closing contact I49B the electronic valve I43 may be effectively shunted.

The remaining switch contacts I49A and I490 are connected to the negative terminal of the source of electrical energy '28 through a grounded conductor I51. Thus the cathodes I44 may be connected to the negative terminal of the source of electrical energy 28 by adjustment of switch I49 so as to close contact I49A or. I490 or the timer system may be disconnected by adjustment I49B andthe opening of'the off-normal switch I31 as shown.

With the switch I49v adjusted to close contact I49A-f or I49C. the electron .fiow fromthe'cathodes 144: to. the; plates I 42.; is: controlled by: grids I45 connected? bye:v conductor I58. to: a. plate I585 of aecondenserlfifl'z The-opposite plate. I61 of the condenser: I60is= connected. by a conductor: I82 tea contacti I63Aiof a normally openswitch. I54 controlled by the electromagnetic relay winding I38. An opposite contact I 63B is connected by a conductor I65 to the conductor I40 and therebyto'thepositive terminalof the source of 'elect'rioal energy 28 throughthe manually operable switch 25 A- conductor I96 leads from-the conductor I62 toethe relay winding II2 which is connected at its oppo'site terminal through agrounded conductor I61to the negative terminal of the-source of electrical energy 28.

Thus energization of relay winding I38- causes in: turn relay I12. to be energized, whereupon switch I24 is actuated to an open position, there-=- by efi'ecting'deenergization of winding I 38;- opening; of switch I64 and deenergization of the stepperrelay winding I I2.

A switcharm I16 is connected to the conductor I66; The switch arm l'lficooperates with switch contacts I'IBA-C. The contacts I'IBB and IIBG are open contacts, while the contact "6A is connected by a conductor IT! to a secondcapacttor. or condenser I78'connected by conductor I-I9 to. the conductor I58 and across the capacitor I60 upon the closing of the switch contact I=T6A so as -to increase the capacity of the timing condenser.

A conductor I80 leads from the conductor I58 tothe stepper relay switch arm I2I-. Thus-the plate I59 of the capacitor I60 is connected by theconductors I58 and I80'to the switch arm I2! which, as previously described, is arranged to close sequentially the contacts I 21A- through I21N.

Leading from the contacts I27A through I21N, respectively, are the resistors I36A-N each of=a value sufiicient to eiTect a predetermined discharge. period for capacitor I60'or time interval for. energizing the electromagnet I9'correspondingsthereto. The resistors IE'SAM may be of different value so as to effect different time intervals of operation for each lcaddevice.

Leading from the opposite terminals of the resistors I36A-N-is the conductor 21. Connected to the conductor 21 by a conductor I 8| is a switch arm I82 for cooperating with contacts I 82A-C. The conductor !8I connects the switch arm'I82 to the-positive terminal of the source of electrical energy 28 through the control switch 25.

Theswitch arm I82 is arranged to selectively contact one of the three contacts includingopen contacts IS2C, contact I82A connected by a conductorl 83t0 the contacts I 27A-M so as to shunt out of the time delay circuit the resistors I36A'M and'contact 1823 connected by an electrical conductor I84 to the resistors ISEEA-M at a point intermediatethe opposite ends of the latter'resisters;

It willbe seen-then-that when the switch arm I8-2 closes the contact I823, a portion of "the resistor" I36 leading from the contacts I TIA-M willbe shunted out of the circuit leadin from the'positive terminal of the source of electrical energy'28 and the plate I59 of the condenser I60. However, upon the switch arm I82 contacting the open contact I620 the full resistance of the resistor I36 leading from the contacts I 21A-M- will be inserted in the latter circuit.

The control switches 64, I49-and I76 are ar ranged-Efor operation in unison from a single control- 1m h 65 operatively connected thereto'by a shaft I85 indicated by dotted lines. The switch I82 is also controlled manually by a knob I81 operatively conected thereto by a shaft I89 and conveniently mounted on the panel of the timer 28.

Operation The foregoing electronic timer is particularly designed for use in conjunction with the manifold type of ice eliminating system for airfoil surfaces of aircraft and is arranged to open the boot inflating valves automatically in the proper sequence for the proper time intervals. Since ice does not form at the same rate or to the same degree on all occasions, a certain flexibility of control has been incorporated to permit the operator to vary certain components of the system to suit the prevailing conditions.

Referring to the drawing of Figure 2, and with the control switches in the position shown, operation is initiated by first closin the switch 25 and thereafter adjusting the control knobs 65 and I81 to one of the operative positions such as the full on and normal air flow positions respectively at which the switch arm i engages contact 12, switch arm Hi9 engages contact I49A and switch arm I'It engages I'lEiA, while switch arm I82 closes contact IBZB through the adjustment of knob I81.

The cathodes I41 are then connected through the switch M9 to the negative terminal of the source of electrical energy 23. The bias applied at the grids I45 is positive at the time the switch I49 is closed since the grids M5 are connected through the switch arm I21 and contact I21N to the positive terminal of the source 28. Thus a large plate current flows effecting energ-ization of the relay winding I38 causing switch I64 to close contacts I53A and I533. The closing of the switch I24 then efiects a charging circuit for the capacitor I65 and I18 in which the electronic flow from the cathodes I44 to the grids I45 and through the conductors I55 applies a negative charge to the plate I59 of the capacitor I68, and like plate of capacitor I18 while a positive charge is applied to the plate IBI and like plate of capacitor I18 through conductors I52, and switch I18, switch I54, conductor 55 and conductor We to the positive terminal of the source of electrical energy 28.

The closed relay switch 584 thus causes the condensers I50 and H18 to become quickly charged and in turn the relay winding II2 to become energized so as to open the switch I24 in the plate circuit.

The opening of the interrupter switch Ii24 then cuts on the plate current, which (is-energizes the relay winding I38 which opens switch I56 and the energizing circuit for the stepper relay winding H2. The spring H8 then draws the armature II3 downward in a counterclockwise direction and eiiects movement of the ratchet gear H6 together with the stepper switches I26 and I21 to a position closing contacts IZiA and I21A respectively and energizing circuit ISA.

Upon the opening of switch I64, the direction of electron flow relative to the condensers I60 and I18 reverses and the condensers I60 and I18 discharge. Thus, upon the opening of switch I64, there is an electron flow to the positively charged plate I6I of the condenser Ito and like plate of condenser I18 through grounded conductor I61, stepper relay winding II2, conductor I56, switch I16 and conductors I52 and I11. The negatively charged plate I59 of the condenser I60 and like plate of condenser I18 discharges through the conductor I58, conductor I85, stepper relay switch I21, contact I21A, portion of resistance I36A, switch I82 and conductor 21 through switch 25 to the positive terminal or the source 28.

The negative charge on the plate I59 of the condenser I68 and like plate of condenser I18 applies a negative bias to the grids I 55 through conductor I58 which is suilicient to keep the grid biased beyond cut off for a predetermined period dependent upon the value of the resistance I35 connected in the discharging circuit through operation of the stepper relay switch I21.

The charge on the condensers I60 and I18 is thus gradually neutralized through the resistance I38 until the bias on the grids I45 becomes sufficiently positive to allow enough plate current to flow to again effect energization of relay Winding I38 so as to close switch E54. The time required is dependent upon the time constant of the resistor I36 and capacitor I68.

When the relay winding I38 is energized closing switch I54, the condenser I50 and condenser I18 are again recharged. The normally open switch IE6 remains closed until the interrupter contacts I24 are opened momentarily by energization of the stepper relay I I2 opening the circuit for the relay winding I38 and de-energizing the stepper relay IE2 so as to cause the stepper switches I26 and I21 to advance to position I263 and I21B respectively. A new timing interval then begins during which circuit 913 is energized.

Similarly the load circuits i9C-I9ivi are energized for time intervals depending upon the value of the then connected resistor I35 and condensers I and I18. However, upon the stepper switch I21 moving to a position closing contact I2'IN, the cam I28 is adjusted so as to position the portion I29, as shown in the drawing, so as to open the off normal switch I31.

If control switch I49 is adjusted so as to close contacts A or C, the cathodes M4, are connected through grounded conductor I51 to the negative terminal of the source 28 and hence in this position of control switch I49, the operation is con tinuous between cycles. If control switch I49 has been returned to the off position so as to engage open contact l ieB then the opening of the off normal switch terminates operation of the timer at the home position since then no power is supplied to the cathode I44. If control switch I82 be adjusted so as to close open contact I820, a high resistance ISBA-M gives a greater delay period of operation for each boot than if switch I82 closes contact I823.

The system normally operates with th inflatable boots in continuous cyclic operation while the heater elements are continuously energized by the alternators 35 and 51 as heretofore described. Upon failure, however, of one of the alternators 35 or 31 as indicated by the extinction of one of the indicator lights 48 or 49, the operator will thereupon adjust the knob 55 from the full on position to the half on position causing switch 64 to close contact 52, switch M9 to close contact I49C, and switch arm Ile to open contact NBA and close open contact I180. The opening of contact I16A causes the condenser I18 to be switched out of the timing circuit so as to decrease all time intervals of inflation or the inflatable boots 3 by a predetermined value of, for example, fifty per cent, while the adjustment of the switch 64 so as to close contact 62 connects the control winding 52 of the reversing relay 55 to the stepper relay switch contacts EBA-F so that the step- 10 per relay switch arm 68 cycles the power from ing indicator means operatively connected to the remaining alternator to half of the heated said generators for indicating failure of the other sections for half of the cycling time and to the of said generators, and operator-operative switch other half of the heated sections for the remainmeans to effectuate the means for operatively ing half of the cycling time so as to assure efconnecting the timer to the control winding upon ficient removal of the ice from the airfoil surfailure of the other of said generators.

faces under such emergency conditions through 3. An ice eliminating system for an aircraft, the joint action of the inflatable boots 3 and the comprising, in combination, two sets of electric resistor heater elements 34. heater elements for effecting the removal of ice Although only one embodiment of the inv nfrom an airfoil surface of said aircraft, a pair tion has been illustrated and described, Various of electric generators, means op ratively c nchanges in the form and relative arrangements necting one of said generators so as to supply 01' the parts may be made to suit requirements. electric energy to one set of said heater elements What is claimed is: and the other of said generators so as to supply 1. For use with an ice eliminating system for electr energy to another Set Of Said heater aircraft of the class including a plurality of inelements, said connecting means including switch flatable ice eliminating members, means for opmeans for transferring the operative connecerating said inflatable members, electric heater tions of said electric generators from one tothe elements embedded in said members for eiTect other of said sets of heater elements, control ing the removal of ice from said members, a pair 0 means for operating said switch means to effect for supplying electric energy to another set of generators for predetermined periods.

said heater elements; means for controlling said 4. The combination defined by claim 3 includinflatable members and heater elements, said ing ind cator m a p r y ct d o control means comprising relay switch means for said generators for indicating failure of one of transferring the operative connections of at Sa d g nera o a d p p ve a s o least one of said electric generators from one e fectuate t mea for p ra v y connecting to the other of said sets of heater elements, a the tim to t c t o m stimer normally operative for providing a se- CHARLES MACINTYRE- quence of predetermined periods of operation of said inflatable members, said relay including a References Cited m the me of thls patent coitiltrol winging for ogerlating saidtswitch means, UN TE STATES PATENTS an means or opera ve y connec ing said timer to said control winding for operating said relay g ggig i Dec gi switch means so as to alternately effect full en- 2393635 g i i 1946 ergization of each of said sets of electric heater 2418205 Ta A 1947 elements by at least said one generator for pe- 2444208 T FT "3 p 1948 riods of operation controlled by said timer. ay or e a une 2. The combination defined by claim 1 includ- 2344310 Lauriceu June 194B 

